1. Field of the Invention
The present invention relates to a vehicle driving torque transmitting system, and more particularly to a system for transmitting a driving torque from a power plant to a vehicle wheel. More specifically, the present invention pertains to means for controlling the torque transmitted to the wheels in such driving torque transmitting system.
2. Description of the Prior Art
In a conventional torque transmitting system, it has been known to provide a slip clutch in a torque transmitting path to control the torque to be transmitted. In one type, there is interposed in the torque transmitting path a wet clutch which includes an input friction member and an output friction member which are forced into engagement under a fluid pressure. The capacity of the wet clutch of transmitting torque is dependent on the value of the fluid pressure so that the torque to be transmitted can be controlled by changing the fluid pressure forcing the friction members into engagement.
In another type, a viscous coupling is interposed in the torque transmitting path. The viscous coupling includes input and output friction plates which are located adjacent to each other with a viscous fluid interposed therebetween. One example of the torque transmitting system using such viscous coupling is shown in the U.S. Pat. No. 3,760,992. In the viscous coupling disclosed by the U.S. patent, the friction plates are formed with openings which determines the torque transmitting capacity. By changing the diameter of the openings, it is possible to obtain viscous couplings of different torque transmitting capacity.
It should be noted that in the conventional torque transmitting system there is always a certain extent of slip between the input and output friction members so that there is a possibility of temperature increase due to generation of heat under the slip movement. There will be no serious problem as long as the temperature increase is within an allowable limit, however, if there is an excessive slip, the temperature increase will be such that the friction plates are damaged under the heat.